Vehicular acceleration sensors for providing an output when an acceleration threshold has been exceeded are known, especially for sensing an acceleration along a particular axis, i.e. in a particular direction. Some attempts have been made to provide so-called omni-directional acceleration sensors which provide an output when an acceleration threshold is exceeded in any direction. Such acceleration sensors are mechanical devices including an inertia weight which somehow triggers an output, usually a mechanical output, when the inertia weight moves with respect to the remainder of the mechanics of the sensor causing the mechanical output to move in a particular direction.
EP0775317 discloses a multi-directional acceleration sensor which provides a mechanical output along an axis, i.e. the mechanical output of the sensor is provided in a particular direction. Since the mechanical output comprises a mechanical element moving in a particular direction, along a particular axis, that element itself will experience acceleration or deceleration along that axis. The acceleration experienced by the mechanical element effecting the mechanical output inevitably leads to the overall mechanism being more sensitive or less sensitive to accelerations or decelerations along the axis of the mechanical output. For example, if the mechanical output is along the x-axis and the sensor experiences a violent deceleration along the x-axis, then the mechanical element providing the mechanical output along the x-axis will experience that deceleration as well as the inertia weight thereby making the sensor more sensitive to decelerations along that x-axis. If an acceleration along the x-axis is provided in the opposite direction to which the mechanical element must move to provide its output, then it will be apparent that the sensor is less sensitive to such an acceleration. Such an acceleration sensor cannot therefore be regarded as truly omni-directional where the output is provided along a particular axis or in a particular direction.
This potential insensitivity or over-sensitivity to acceleration in a particular direction is called a “cross-talk” error for ease of reference. Cross-talk error occurs when an acceleration or a component of acceleration along a particular axis is aligned with a linear movement of a mechanical element in the trip mechanism or output mechanism of the acceleration sensor.
It is an object of the present invention to seek to provide an acceleration sensor which is omni-directional and which is not reliant on a mechanical output being provided along a particular axis.